You can try to increase the number of predicted fragments within the MS Fragmenter Options, or increase the number of fragmentation steps. You might also consider switching on some of the Specific Fragmentation rules that are off by default. If you increase the number of selected rules, you should also consider increasing the Maximum Number of Fragments Generated on Each Step as well.

Finally, ACD/MS Fragmenter is a rules-based predictor, and is based on well-documented fragmentation rules reported in the literature. It is possible that the fragment isn't predicted by the MS Fragmenter rule set.

Open ACD/MS Fragmenter. In the bottom left corner, click 4-Options. In the window that appears, in the bottom right corner, click Help. In the Help window, use the tabs and the hyperlinks in the table to review the rules.